Balanced phase shift transformer

ABSTRACT

981,517. Transformers. PHILIPS ELECTRONIC &amp; ASSOCIATED INDUSTRIES Ltd. June 12, 1963 [June 13, 1962], No. 23410/63. Heading H1T. A balanced phase-shift transformer has a primary winding 4 on a first former 1 and a centretapped secondary 7 on a second former 2, the centre tapping point being connected, preferably through a resistance, to a tertiary winding (having leads 11) on former 2 and the primary being connected in series with a further (coupling) winding via conductor 12, the further winding and the tertiary winding being wound together bifilarly to form the coil at 8. The secondary 7 may consist of two conductors wound bifilarly and connected in series. Movable cores 13 and 14 may be provided for varying the inductances of the primary and secondary windings respectively, while the coupling between the coupling winding and the secondary winding may be varied, without substantially affecting the inductance of the coupling winding, by a movable core 14. The transformer and the associated circuit illustrated may be enclosed in a metal screening container having a partition screening off winding 4 and holes giving access to the adjustable cores.

P. T. RUDGE Filed June 12,

INVENTOR.

PETE R T. R yo GE BALANCED PHASE SHIFT TRANSFORMER an} 1 l.

United States Patent 3,319,154 BALANCED PHASE SHIFT TRANSFORMER Peter Thompson Rudge, Hawthorndeue, South Australia,

Australia, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed June 12, 1963, Ser. No. 287,363 Claims priority, application Australia, June 13, 1962, 18,810/ 62 Claims. (Cl. 323-48) The present invention provides an improved balanced phase shift transformer of the type used in ratio detector circuits and other circuits employed for demodulating angle modulated signals.

The function of a balanced phase shift transformer is well known and the construction of one type of balanced phase shift transformer for use in a ratio detector circuit is illustrated in Figure 9 of an article in R.C.A. Review, June 1947, pages 201 to 236.

The balanced phase shift transformer illustrated in the above mentioned Figure 9 has a number of disadvantages. For example, adjustment of the primary winding inductance and adjustment of the secondary winding inductance can only be made conveniently from opposite ends of the transformer. Furthermore, there is no separate adjustment provided for varying the coupling between the primary winding and the secondary winding and in addition the dimensions of a transformer generally constructed in the manner illustrated are not suitable in particular applications. The present invention overcomes these disadvantages.

A balanced phase shift transformer in accordance with the invention may be constructed so that the inductance of the primary winding and the inductance of the secondary winding may both be adjusted conveniently from the same end of the transformer, and provision may be made for a separate adjustment for varying the coupling between the primary Winding and the secondary winding. In addition a transformer in accordance with the invention may be constructed having dimensions which make it more suitable for certain applications than the balanced phase shift transformer illustrated in the aforementioned Figure 9.

The balanced phase shift transformer in accordance with the invention comprises an input circuit having a first winding wound on a first former and a center tapped secondary winding wound on a second former. The center tap of the secondary winding is connected to one end of a tertiary winding preferably, but not necessarily, via a resistance, and the first winding is connected in series with a further winding. The invention is characterized in that the said tertiary winding and the said further winding are bifilarly wound together on the second former.

Preferably, the two halves of the center tapped secondary winding consists of the two conductors of a bifilar winding connected so as to function as a single conductor winding having a tapping at its center point.

In order that the invention may readily be carried into effect, one embodiment thereof will now be described more fully, by way of example, with reference to the accompanying drawing, in which:

The single figure illustrates in diagrammatic form a balanced phase shift transformer in accordance with the invention and connected so as to form part of a ratio detector circuit. The portion of the figure surrounded by dashed lines represents a cross-section view of the balanced phase shift transformer.

Referring now to the figure, a first former 1 and a second former 2 are mounted side by side on a suitably shaped base 3 of insulating material. The former 1 and the former 2 are of a hollow cylindrical shape and are made of insulating material suitable for the purpose. The internal surface of the former 1 and the former 2 are each threaded so as to accommodate one or more threaded cores of ferromagnetic material.

A winding 4 is provided on former 1. The winding 4 consists of a single conductor 5 (the ends only of which are shown) wound on the external surface of former 1.

A winding 7 and a winding 8 are provided on the former 2. The Winding 7 consists of two conductors, a conductor 9 and a conductor 10, bifilarly wound together on the external surface of former 2. The ends only of the conductor 9 and the conductor 10 are shown. The Winding 8 consists of two conductors also, a conductor 11 and a conductor 12. Conductor 11 and conductor 12 are also bifilarly wound together on the external surface of former 2. The ends only of the conductor 11 and the ends only of conductor 12 are shown.

Wire consisting of two conductors insulated from each other and suitable for providing two bifilarly wound condoctors on a former is known. Such wire is commonly referred to as bifilar wire.

The winding 7 and the winding 8 may be formed from bifilar Wire. For the sake of convenience during the winding of winding '7 and winding 8, the balanced phase shift transformer should be so designed that similar gauge bifilar wire is used for the winding 7 and for the winding 8.

A core 6 is provided within the former 1 and a core 13 and a core 14 are provided within the former 2. The cores 6, 13 and 14 are made of ferromagnetic material and are each of a cylindrical shape. The cylindrical surface of each of the cores 6, 13 and 14 is threaded for engagement with the threaded internal surface of the former within which it is provided.

A slot may be provided at one or both ends of each of the cores 6, 13 and 14 to enable the cores to be rotated by means of a screwdriver or a similar tool in such a manner that the position of the cores within the formers is adjusted.

The core 13 is provided within former 2 in the vicinity of that portion of former 2 which is surrounded by wind ing 7.

The core 14 is provided within former 2 within that portion of former 2 which is surrounded by winding 8. The length of core 14 is shorter than the length of winding 8 and the transformer is designed so that core 14 remains within that portion of former 2 surrounded by winding 8 for the whole of the required adjustment range of core 14.

The former 1 and the former 2 are housed within a metal screening container indicated by dashed lines 32 which surrounds both of the formers and has a screening partition indicated by dashed lines 33, which screens winding 4 from winding 7 and winding 8. Holes are provided in the screening container for gaining access to the core 6 and the core 13 from the end of former 1 and former 2 remote from base 3. A hole is provided in the base 3 for gaining access to core 14.

In the embodiment of the invention being described, it is intended that the whole of the circuit arrangement illustrated in the figure be mounted within the abovementioned screening container in such a manner that the circuit arrangement is provided as a single unit having two input terminals 15 and 16 and two output tremiuals 17 and 18. It will be apparent however that it is not essential for the whole of the circuit arrangement illustrated in the figure to be housed in a single container and, for the sake of clarity, the circuit elements of the ratio detector circuit are shown external to the screening container.

The conductor 5 and core 6 of the winding 4 serves to adjust the overall primary inductance of the phase shift transformer and the conductor 9 and the conductor 10 former.

serve as the secondary winding of the phase shift trans- The end of conductor 9 adjacent to the base 3 is connected to the end of conductor 10 remote from the base 3 in such a manner that conductor 9 and conductor 10 are connected in series and serve as a single conductor winding having a center tap at its center point.

The end of conductor 9 remote from the base 3 is connected to the anode of diode 20 and the end of conductor 10 adjacent to the base 3 is connected to the cathode of diode 19.

The conductor 11 of winding "8 serves as a tertiary winding. The end of conductor 11 adjacent to the base 3 is connected via a resistance 31 to the junction of conductors 9 and 10 of winding 7 and the end of conductor 11 remote from the base 3 is connected to the junction of capacitors 22 and 23 and to ground via terminal 18.

The conductor 12 of winding 8 serves as a coupling or primary winding.

The ends of conductor and conductor 12 remote from the base 3 are connected to terminal-s 15 and 16, respectively, and the ends of conductor 5 and conductor 12 adjacent to the base 3 are connected together so that conductor 5 and conductor 12 are connected in series across input terminals 15 and 16.

By means of the coupling winding formed by conductor 12, the series combination of the inductive winding formed by conductor 5 and the coupling winding formed by con ductor 12 are coupled to the secondary winding formed by conductors 9 and and to the tertiary winding formed by conductor 11.

By means of core 6 the inductance of the input circuit formed by conductor 5 and conductor 12 may be varied and by means of core 13 the inductance of the secondary winding formed by the series combination of conductor 9 and conductor 10 may be varied. By means of core 14 the distance between core 13 and core 14 may be adjusted thereby enabling the coupling .to be varied between the coupling winding formed by conductor 12 and the secondary winding formed by conductors 9 and 10.

Since the core 14 remains within the portion of former 2 surrounded by winding 8 for the whole of the required adjustment range of core 14, the coupling between the coupling winding formed by conductor 12 and the secondary winding formed by conductors 9 and 10 may be adjusted within this range substantially without affecting the inductance of the coupling winding and hence without substantially affecting the overall inductance of the series combination of the winding 4 and the coupling winding.

When the balanced phase shift transformer represented by the portion of the figure surrounded by dotted lines is connected for operation as part of a circuit arrangement for the detection of angle modulated signals, it is intended that the series combination of the winding formed by conductor 5 and the coupling winding formed by conductor 12 be connected to a source of angle modulated signals in the same manner that the primary winding of a known type of balanced phase shift transformer (e.g., the balanced phase shift transformer illustrated in Figure 9 of the aforementioned article in RCA Review) is usually connected. It is also intended that the secondary winding formed by the conductors 9 and 10 and the tertiary winding formed by conductor 11 be connected to form with other components the remainder of the circuit arrangement in the same manner that the secondary winding and the tertiary winding of a known type of balanced phase shift transformer is usually connected to form the remainder of such a circuit arrangement.

In the figure, the balanced phase shift transformer shown within the dashed lines 32 is connected for operation as part of a ratio detector circuit. The series combination of the winding formed by conductor 5 and the coupling winding formed by conductor 12 are connected between input terminal-s 15 and 16 which may be connected to a source of frequency modulated signals. The

secondary winding formed by conductors 9 and 10 and the tertiary winding formed by conductor 11 are connected to form together with diodes 19 and 20, capacitances 21, 22, '23, 24, 29 and 30 and resistances 25, 26, 27, 28 and 31 the remainder of the ratio detector circuit.

With the exception of the balanced phase shift transformer and the resistance 31, the circuit illustrated in the figure is well known to persons skilled in the art and so it is not considered necessary at this point to describe the operation of the circuit.

In the aforementioned article in RCA Review, methods of reducing the balanced A.M. component in the output of a ratio detector are described. One of the methods described consists of connecting a resistance of suitable value in series with the tertiary winding of the balanced phase shift transformer. The resistance is connected in series wit-h the lead between the end of the tertiary winding electrically remote from the secondary winding and the output circuit of the ratio detector of which the balanced phase shift transformer forms a part.

With a balanced phase shift transformer embodying the present invention, a resistance may in. the same manner be connected in the lead from the end of the tertiary winding remote from the secondary winding to the output circuit of the ratio detector of which the balanced phase shift transformer forms a part. To accomplish this in the case of the figure, a resistance would be connected in series with the lead between the junction of capacitances 22 and 23 and the end of conductor 11 remote from the base 3. The end of conductor 11 adjacent to the base 3 would be connected directly to the junction of conductors 9 and 10, not via the resistance 31, as illustrated.

It has been found however that in a ratio detector circuit including a balanced phase shift transformer embodying the invention, that the unbalanced A.M. component in the output of the ratio detector can be reduced further if a resistance is provided in the lead connecting the center tap of the secondary winding to the tertiary winding instead of in the lead from the end of the tertiary winding electrically remote from the secondary winding to the output circuit of the ratio detector. To accomplish this in the embodiment shown in the figure, resistance 31 is provided in the lead from the junction of conductors 9 and 10 and the end of conductor 11 adjacent to the base 3.

What is claimed is:

1. A transformer comprising first and second spaced apart support members, an input circuit comprising first and second serially connected winding portions wound on said first and second support members, respectively, an output winding having a center tap wound on said second support member so as to be magnetically decoupled from said first winding portion, a tertiary winding wound on said second support member so as to form a bifilar winding with said second winding portion, and means connecting one end of said tertiary winding to the center tap of said output winding.

2. A transformer as claimed in claim 1 wherein said connecting means comprises a resistance element.

3. A transformer as claimed in claim 1 wherein said output winding comprises first and second conductors wound together to form a bifilar winding and connected together to form a single winding having a center tap which divides said winding into two identical halves.

4. A transformer as claimed in claim 1 wherein said first and second support members are hollow and further comprising a first ferromagnetic core movably mounted within said first support member adjacent said first 'Wll'lding portion for independently adjusting the inductance of said input circuit and a second ferromagnetic core movably mounted within said second support member adjacent said output winding for independently adjusting the inductance of said output winding.

5. A transformer as claimed in claim 4 further comprising means for varying the coupling between said second winding portion and said output winding, said varying means comprising a third ferromagnetic core movably mounted within said second support member adjacent said second winding portion and movable with respect to said second ferromagnetic core, said third ferromagnetic core and said second support member being cooperatively arranged to limit the range of travel of said third ferromagnetic core so as to confine its movement within said second winding portion whereby the inductance of said second Winding portion remains substantially constant.

6. A transformer as claimed in claim 3 wherein said connecting means comprises a resistance element.

7. A transformer as claimed in claim 5 wherein said output winding comprises first and second conductors wound together to form a bifilar winding and connected together to form a single winding having a center tap which divides said winding into two identical halves.

8. A transformer as claimed in claim 5 wherein said connecting means comprises a resistance element.

9. A transformer as claimed in claim 3 wherein said first and second conductors of the output winding and said tertiary winding and said second winding portion consist of similar gauge bifilar wire.

10. A transformer as claimed in claim 7 further comprising a common conductive housing surrounding said transformer and including a conductive partition member separating said first and second support members.

11. A balanced phase shift transformer comprising first and second substantially parallel, spaced tubular coil formers having longitudinal axes, a primary circuit comprising first and second serially connected winding portions mounted on said first and second coil formers, respectively, a secondary winding having a center tap and mounted on said second former so as to be axially spaced from said second winding portion and magnetically decoupled from said first winding portion, a tertiary winding mounted on said second coil former generally coextensive with said second winding portion so as to form therewith a bifilar winding, and means connecting one end of said tertiary winding to the center tap of said secondary winding.

12. A transformer as described in claim 11 wherein said secondary winding comprises first and second serially connected conductors Wound together to form a bifilar winding.

13. A transformer as described in claim 12 further comprising a first ferromagnetic core mounted within said first coil former adjacent said first winding portion, a second ferromagnetic core mounted within said second coil former adjacent said secondary winding, and a third ferromagnetic core mounted within said second coil former adjacent said second winding portion.

14. A transformer as claimed in claim 13 wherein each of said first, second and third ferromagnetic cores are axially movable within their respective coil formers thereby to adjust the inductance of said primary circuit, the inductance of said secondary winding, and the coupling between said second winding portion and said secondary winding, respectively, said third ferromagnetic core having an axial dimension which is less than the axial length of said second winding portion whereby a range of adjustment of said third ferromagnetic core exists within which the inductance of said second winding portion remains substantially constant.

15. A transformer as described in claim 14 wherein said connecting means further comprises a resistance element.

References Cited by the Examiner UNITED STATES PATENTS 2,364,558 12/ 1944 Stocker 323-48 X 2,501,077 3/1950 Muraka-mi 329- 2,544,508 3/1951 Mackey 336-l31 X 2,595,441 5/1952 Avins 329129 X 2,798,152 7/1957 Janssen 329129 X 2,849,690 8/1959 Verhoeven 336--131 X 2,883,614 4/1959 Ehret 323-109 2,937,274 5/ 1960 Horowitz 329-129 X 3,011,138 11/1961 Analek 336131 X 3,047,813 7/ 1962 Danker 329-129 JOHN F. COUCH, Primary Examiner.

LLOYD MCCOLLUM, Examiner. W. E. RAY, W. H. BEHA, Assistant Examiners, 

1. A TRANSFORMER COMPRISING FIRST AND SECOND SPACED APART SUPPORT MEMBERS, AN INPUT CIRCUIT COMPRISING FIRST AND SECOND SERIALLY CONNECTED WINDING PORTIONS WOUND ON SAID FIRST AND SECOND SUPPORT MEMBERS, RESPECTIVELY, AN OUTPUT WINDING HAVING A CENTER TAP WOUND ON SAID SECOND SUPPORT MEMBER SO AS TO BE MAGNETICALLY DECOUPLED FROM SAID FIRST WINDING PORTION, A TERTIARY WINDING WOUND ON SAID SECOND SUPPORT MEMBER SO AS TO FORM A BIFILAR WINDING WITH SAID SECOND WINDING PORTION, AND MEANS CONNECTING ONE END OF SAID TERTIARY WINDING TO THE CENTER TAP OF SAID OUTPUT WINDING. 